We investigated the precise crystal structures and electronic states in a quasi-two-dimensional molecular conductor α-(BETS)2I3 at ambient pressure. The electronic resistivity of this molecular solid shows a metal-to-insulator (MI) crossover at 𝑇 MI = 50 K. Our x-ray diffraction and 13 C nuclear magnetic resonance experiments revealed that α-(BETS)2I3 maintains the inversion symmetry below 𝑇 MI . The first-principles calculations found a pair of anisotropic Dirac cones at a general k-point, where the degenerated contact points are located at the Fermi level. Furthermore, the origin of the insulating state in this system is explained by a small energy gap of ~2 meV opened by a spin-orbit interaction, in which the Z2 topological invariants indicate a weak topological insulator. Our results suggest that α-(BETS)2I3 is a promising material for studying the bulk Dirac electron system in two-dimension.

Using first-principles calculations, we found the topological phase transition induced by electric fields in one-bilayer Bi(111). The bandgap decreased with increasing electric field strength, and it is closed at 2.1 V/Å. For fields exceeding 2.1 V/Å, the bandgap increased with increasing electric field strength, reaching 0.34 eV at 4.0 V/Å. We computed the Z 2 invariant that characterizes topological insulator phases. As results, one-bilayer Bi(111) showed a topological phase transition induced by the electric field, from the topological insulator phase to the trivial insulator phase through a Dirac semimetal. This topological phase transition could be applied to novel devices. *

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A sizable transverse thermoelectric coefficient N , large to the extent that it potentially serves applications, is predicted to arise, by means of first-principles calculations, in a Skyrmion crystal assumed on EuO monolayer where carrier electrons are introduced upon a quantum anomalous Hall insulating phase of Chern number C = 2. This encourages future experiments to pursue such an effect.

We performed first-principles simulations to elucidate the transverse thermoelectric effect (anomalous Nernst effect) of the half-metallic FeCl 2 monolayer. We analyzed its thermoelectricity based on the semiclassical transport theory including the effect of Berry curvature and found that carrier-doping induced a large anomalous Nernst effect that was ∼6.65 μV/K at 100 K if we assumed 10 fs for the relaxation time. This magnitude originates in a large Berry curvature at the K-point of a hexagonal Brillouin zone. These results suggest that two-dimensional ferromagnetic half-metallic materials can potentially be used in thermoelectric devices.